It is well known in the art to digitize speech by performing digital encoding and decoding. For example, Motorola, Inc., Phoenix, Arizona, markets its MC3517/18 series of semiconductor devices, designed for military secure communications devices and commercial telephone applications. This device utilizes a continuously variable slope delta (CVSD) modulator/demodulator, with a sensitive linear multiplier to change the slope of the delta modulator integrator. The circuit is described in the "Specifications and Applications Information" data sheet for the product, which notes that the CVSD circuitry provides increased dynamic range by adjusting the gain of the integrator. Insofar as applicant is aware, this Motorola product is not designed for use as a frequency multiplier.
Voice processing apparatus are known, such as, for example, those described in U.S. Pat. Nos. 4,121,058, 2,183,248, 2,943,152, 3,863,026, 3,104,284, 3,621,150, 3,920,905, 3,936,610, 3,949,175, 3,965,298, 3,976,842, 3,949,175, 3,634,625, 3,295,107, 3,949,174, 3,681,756 and 3,621,150.
In the apparatus described in U.S. Pat. No. 4,121,058, for example, audio data is converted to a digital format at a selectable conversion rate and applied through a microprocessor into memory storage. Stored data is selectively recalled and reconverted into an analog format for reconstruction into human speech at a processing rate independent of the input storage rate.
Another device on the market today is the VSC M8 series module sold by VSC Corporation, San Francisco, Calif. This device, described in the data sheet for the product, and apparently the subject of U.S. Pat. No. 3,786,195, uses bucket brigade devices in a single-channel configuration to achieve low-cost speech compression.
Notwithstanding the known art, there exists a need for a low-cost frequency multiplication apparatus which performs frequency multiplication with an acceptable dynamic range. There further exists a need for a frequency multiplication apparatus wherein the multiplication rates may be either greater or lower than unity. The need further exists for an apparatus to fulfill these needs whose design is such that all active elements may be included on a single large scale integrated circuit (LSI) chip. Such a device would find a ready demand in such applications, by way of example only, as music synthesizers music apparatus, and hand-held voice pitch shifting devices.